Windsor Castle PMP ?
New London heli routes chart is out. The only change appears to be a piece of prohibited airspace over Windsor - to an alt of 200ft !
Notwithstanding the fact that the Castle probably reaches 175ft AMSL, the airspace surely only affects very low dep/arr on 27R/09L.
And what does PMP mean ?
Permanent Majesty Prohibition ?
Peasants Must Pay ?
From memory it is a Provost Marshal's Prohibited area, mandatory for military flights and, I believe, not relevant to civil aircraft. I think all the royal palaces and some other sensitive locations have them.